1. Field of the Invention
The present invention relates to a chain tensioner which includes a tensioner body having a plunger housing hole opened at one end, a cylindrical plunger to be slidably inserted into the plunger housing hole, and biasing means for biasing the plunger in a protruding direction, and which holds tension of a chain at a proper value.
2. Description of the Related Art
Conventionally, it is common practice to use a chain tensioner that holds tension of a chain at a proper value. For example, there is a known chain guide mechanism that uses a travel guide shoe to slidingly guide a transmission chain such as a roller chain being endlessly wound around sprockets respectively provided on a crankshaft and a camshaft inside an engine room, wherein a swinging chain guide that includes the travel guide shoe is biased by a chain tensioner in order to hold tension of the chain at a proper value.
For example, as shown in FIG. 11, a timing chain CH is endlessly wound between a drive sprocket S1 mounted to a crankshaft and a pair of driven sprockets S2 and S3 mounted to a camshaft inside an engine room, and the timing chain CH is guided by a swinging chain guide G1 and a fixed chain guide G2 to constitute a chain guide mechanism.
The fixed chain guide G2 is fixed inside the engine room by two mounting shafts B1 and B2, and the swinging chain guide G1 is mounted inside the engine room to be swingable within a winding plane of the timing chain CH around a mounting shaft B0.
A chain tensioner 500 holds tension of the timing chain CH at a proper value and suppresses vibration by pressing the swinging chain guide G1.
As the known chain tensioner 500 that is used in such chain guide mechanisms, a chain tensioner is known in which: a plunger is used which includes, on an outer peripheral surface thereof, a plurality of annular grooves that are engageable by an elastic ring member; a ring holding portion that holds the elastic ring member is provided on an open side of a plunger housing hole, and the elastic ring member is held by the ring holding portion and elastically engages the annular grooves of the plunger to constitute a ratchet-type backstop mechanism (refer to Japanese Patent Application Laid-open No. 2002-5249, Japanese Patent Application Laid-open No. 2001-146946, and the like).
Maintenance work of a chain guide mechanism using such a chain tensioner 500 may involve adjusting a position of the plunger by enlarging a diameter of the annular elastic portion of the elastic ring member. In doing so, the diameter of the annular elastic portion of the elastic ring member is to be enlarged through a maintenance hole in a state where the chain tensioner is mounted to an engine or the like.
In addition, even during assembly of the chain tensioner, after the elastic ring member is set to the ring holding portion, the diameter of the annular elastic portion of the elastic ring member is enlarged and the plunger is inserted.